Alkyl ester spotting fluid compositions for differential sticking

ABSTRACT

Alkyl ester spotting fluid compositions and processes for freeing differentially stuck pipe are provided. An alkyl ester spotting fluid composition includes an invert emulsion having an alkyl ester as the external phase and water as the internal phase. In some embodiments, the alkyl ester spotting fluid composition may include the alkyl ester invert emulsion and an emulsifier. The alkyl ester spotting fluid composition may be introduced downhole in the vicinity of a portion of a differentially stuck pipe such that the spotting fluid composition contacts the mudcake and frees the differentially stuck pipe.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims priority from U.S. Provisional Application No.62/292,649 filed Feb. 8, 2016, and titled “ALKYL ESTER SPOTTING FLUIDCOMPOSITIONS FOR DIFFERENTIAL STICKING.” For purposes of United Statespatent practice, this application incorporates the contents of theProvisional application by reference in its entirety.

BACKGROUND

Field of the Disclosure

Embodiments of the disclosure generally relate to downhole treatmentfluids and, more specifically, spotting fluids used to freedifferentially stuck pipe in a well.

Description of the Related Art

Drilling and production systems are employed to access and extracthydrocarbons from hydrocarbon reservoirs in geologic formations. Duringthe course of drilling a well, pipe inserted into the well may becomestuck such that the pipe is unable to be rotated or reciprocated.Differentially stuck pipe, such as a drill string or casing, occurs whena pressure differential across a permeable zone of the formation causesa vacuum seal which locks the drill string or casing in place. In someinstances, lubrication fluids, dehydrating agents such as anhydrousglycols, and acids, either alone or in combination, may be used in anattempt to free the differentially stuck pipe. For example, dehydratingagents may be used to dehydrate the filter cake to assist in relivepressure and break the vacuum seal against the permeable zone of theformation.

SUMMARY

Spotting fluids may be used to free differentially stuck pipe (forexample, drill string or casing) in a well. Pipe inserted in a wellboremay become sealed against a geologic formation due to the buildup ofmaterial (for example, a filter cake) around a portion of the pipe. Aspotting fluid is introduced to remove or reduce this seal and free thestuck pipe. However, preparation and use of existing spotting fluids maybe time-consuming and require hours of soak time to be effective. Somespotting fluids may use corrosive fluids to reduce or remove the seal ofthe filter and may not be readily biodegradable, and the use of suchspotting fluids may require removal from the mud system after recoveringstuck pipe.

In some embodiments, a spotting fluid composition for freeingdifferentially stuck pipe in a well is disclosed. The spotting fluidcomposition includes an emulsifier and an invert emulsion that includesan external phase having an alkyl ester produced from the esterificationof a vegetable oil and an internal phase having water. In someembodiments, the alkyl ester includes at least one of an oleic sunfloweroil ester, a canola oil ester, a jojoba oil ester, and a castor oilester. In some embodiments, the invert emulsion consists of the externalphase having the alkyl ester and the internal phase having water. Insome embodiments, the external phase consists of the alkyl ester and theinternal phase consists of water. In some embodiments, the volumetricratio of the alkyl ester to water is in a range of 95:5 to 60:40. Insome embodiments, the emulsifier is at least 8% by volume. In someembodiments, the alkyl ester is at least 60% by volume, the emulsifieris at least 8% by volume, and water is no more than 32% by volume. Insome embodiments, the spotting fluid composition includes a weightingagent. In some embodiments, the weighting agent includes at least one ofbarite, calcium carbonate, and hausmannite ore.

In some embodiments, a method of freeing a differentially stuck pipe isdisclosed. The method includes introducing a spotting fluid compositionin the vicinity of a portion of differentially stuck pipe, such that thespotting fluid contacts a material surrounding the portion ofdifferentially stuck pipe. The spotting fluid composition includes anemulsifier and an invert emulsion that includes an external phase havingan alkyl ester produced from the esterification of a vegetable oil andan internal phase having water. In some embodiments, the alkyl esterincludes at least one of an oleic sunflower oil ester, a canola oilester, a jojoba oil ester, or a castor oil ester. In some embodiments,the invert emulsion consists of the external phase having the alkylester and the internal phase having water. In some embodiments, theexternal phase consists of the alkyl ester and the internal phaseconsists of water. In some embodiments, the method includes allowing thespotting fluid composition to interact with the material surrounding theportion of differentially stuck pipe over a time period. In someembodiments, the method includes adding the spotting fluid compositionto a mud system configured to circulate a drilling mud. In someembodiment, the spotting fluid compositing is added to the mud system ina range of 2% to 4% by volume. In some embodiments, the method alsoincludes recovering the stuck pipe and retaining the spotting fluidcomposition in the mud system after recovering the stuck pipe. In someembodiments, the volumetric ratio of the alkyl ester to water of theinvert emulsion is in the range of 95:5 to 60:40. In some embodiments,the emulsifier is at least 8% by volume. In some embodiments, the alkylester is at least 60% by volume, the emulsifier is at least 8% byvolume, and water is no more than 32% by volume. In some embodiments,the spotting fluid composition includes a weighting agent. In someembodiments, the weighting agent includes at least one of barite,calcium carbonate, and hausmannite ore.

In some embodiments a method of forming a spotting fluid composition forfreeing differentially stuck pipe is provided. The method includespreparing an invert emulsion that includes an external phase having analkyl ester produced from the esterification of a vegetable oil and aninternal phase having water. The method also includes adding anemulsifier to the invert emulsion to form the spotting fluidcomposition. In some embodiments, the alkyl ester includes at least oneof an oleic sunflower oil ester, a canola oil ester, a jojoba oil ester,or a castor oil ester. In some embodiments, the invert emulsion consistsof the external phase having the alkyl ester and the internal phasehaving water. In some embodiments, the external phase consists of thealkyl ester and the internal phase consists of water. In someembodiments, the volumetric ratio of the alkyl ester to water is in arange of 95:5 to 60:40. In some embodiments, the emulsifier is at least8% by volume. In some embodiments, the alkyl ester is at least 60% byvolume, the emulsifier is at least 8% by volume, and water is no morethan 32% by volume. In some embodiments, the spotting fluid compositionincludes a weighting agent. In some embodiments, the weighting agentincludes at least one of barite, calcium carbonate, and hausmannite ore.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood with regard to the followingdescriptions, claims, and accompanying drawings. It is to be noted,however, that the drawings illustrate only several embodiments of thedisclosure and are therefore not to be considered limiting of thedisclosure's scope as it can admit to other equally effectiveembodiments.

FIG. 1 is a flowchart of a process for determining the sticking bondmodulus (SBM) and ultimate sticking bond strength (USBS) of a mudcakebefore interaction with any spotting fluid;

FIG. 2 is a flowchart of a process for determining the sticking bondmodulus and ultimate sticking bond strength of a mudcake afterinteraction with a spotting fluid composition;

FIG. 3 is a graph of the pulling force versus (vs.) displacement forunsticking the spherical foot from the mudcake without interaction witha spotting fluid;

FIGS. 4A and 4B are graphs of the pulling force vs. displacement forunsticking the spherical foot from the mudcake in the presence of afirst commercial spotting fluid composition;

FIGS. 5A and 5B are graphs of the pulling force vs. displacement forunsticking the spherical foot from the mudcake in the presence of asecond commercial spotting fluid composition;

FIGS. 6A and 6B are graphs of the pulling force vs. displacement forunsticking the spherical foot from the mudcake in the presence of analkyl ester spotting fluid composition;

FIG. 7 is a bar graph showing the sticking bond modulus of a mudcakewithout interaction with any spotting fluids and the sticking bondmoduli associated with commercial spotting fluid compositions and analkyl ester spotting fluid composition;

FIG. 8 is a bar graph showing a comparison of the sticking bond modulusof a mudcake without interaction with any spotting fluids and thesticking bond moduli associated with commercial spotting fluidcompositions and an alkyl ester spotting fluid composition;

FIG. 9 is a bar graph showing the ultimate sticking bond strength of amudcake without interaction with any spotting fluids and the ultimatesticking bond strengths associated with commercial spotting fluidcompositions and an alkyl ester spotting fluid composition;

FIG. 10 is a bar graph showing a comparison of the ultimate stickingbond strength of a mudcake without interaction with any spotting fluidsand the ultimate sticking bond strengths associated with commercialspotting fluid compositions and an alkyl ester spotting fluidcomposition; and

FIG. 11 is a flowchart of a process for freeing differentially stuckpipe using an alkyl ester spotting fluid composition in accordance withan embodiment of the disclosure.

DETAILED DESCRIPTION

The present disclosure will now be described more fully with referenceto the accompanying drawings, which illustrate embodiments of thedisclosure. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to the illustratedembodiments set forth in the disclosure. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the disclosure to those skilled in the art.

The present disclosure includes compositions for use as spotting fluidsand methods to free differentially stuck pipe in a well. The spottingfluid compositions and methods described in this disclosure may freedifferentially stuck pipe by removing or reducing the seal against aformation by material (for example, a mudcake, also referred to as a“filter cake”) around the differentially stuck pipe.

The present disclosure includes alkyl ester spotting fluid compositionshaving an alkyl ester invert emulsion. In some embodiments, the alkylester may be a vegetable ester derived from vegetable material. As usedherein, the term “vegetable ester” refers to an ester produced byesterification of a vegetable oil. In some embodiments, the vegetableester can be produced from a vegetable oil such as sunflower oil, jojobaoil, canola oil, castor oil, palm oil, soybean oil, or other suitableoils. Accordingly, in some embodiments, the alkyl ester can include anoleic sunflower oil ester (for example, a low oleic sunflower oil ester(70% or less oleic acid) or a high oleic sunflower oil ester (greaterthan 70% oleic acid)), a canola oil ester, a jojoba oil ester, or acastor oil ester. In some embodiments, the alkyl ester is produced froma complete esterification of a vegetable oil. In some embodiments, thealkyl ester is produced from a complete esterification of sunflower oil(for example, a high oleic sunflower oil). In some embodiments, thealkyl ester is produced by reacting high oleic sunflower oil with methylalcohol in the presentence of a sodium hydroxide (NaOH) catalyst.

In some embodiments, an alkyl ester spotting fluid composition may beformed from an invert emulsion having an alkyl ester as the externalphase and water (for example, freshwater or seawater) as the internalphase. In some embodiments, the alkyl ester spotting fluid compositionmay include the alkyl ester invert emulsion and an emulsifier. In someembodiments, the spotting fluid composition may also include a weightingagent.

In some embodiments, the alkyl ester spotting fluid composition may beintroduced downhole in the vicinity of a differentially stuck pipe. Insome embodiments, the alkyl ester spotting fluid composition may beallowed to soak for a time period, to affect (for example, weaken,damage, and degrade) the bonds between the mudcake and the stuck pipe.

Examples

The following examples are included to demonstrate embodiments of thedisclosure. It should be appreciated by those of skill in the art thatthe techniques and compositions disclosed in the example which followsrepresents techniques and compositions discovered by the inventors tofunction well in the practice of the disclosure, and thus can beconsidered to constitute modes for its practice. However, those of skillin the art should, in light of the present disclosure, appreciate thatmany changes can be made in the specific embodiments which are disclosedand still obtain a like or a similar result without departing from thespirit and scope of the disclosure.

The following non-limiting example of an alkyl ester spotting fluidcomposition was tested and compared against two commercial spottingformulations. The tested spotting fluid composition includes an invertemulsion having an alkyl ester as the external phase and freshwater asthe internal phase, and an emulsifier. In the example described infra,the alkyl ester is a high oleic sunflower oil ester (greater than 70%oleic acid), and the emulsifier is EZ Spot® manufactured by Halliburtonof Houston, Tex., USA.

Table 1 shows example spotting fluid compositions for use in the field(in the amount of 100 barrels (bbl)) and the laboratory (in the amountof 350 cubic centimeters (cc)):

TABLE 1 Compositions of Field and Laboratory Spotting Fluids FieldFormulation Concentration Lab Formulation Components (bbl) (volume %)(cc) Alkyl Ester 64 64 224 EZ Spot ® 8 8 28 Water 28 28 98 Total Volume100 350

The alkyl ester spotting fluid composition was tested against a firstcommercial spotting fluid that included the EZ Spot® commercialpipe-freeing agent. The first commercial spotting fluid compositions foruse in the field (in the amount of 100 barrels (bbl)) and the laboratory(in the amount of 350 cubic centimeters (cc)) are shown in Table 2:

TABLE 2 Formulation of First Commercial Spotting Fluid Field FormulationConcentration Lab Formulation Components (bbl) (volume %) (cc) Diesel 6464 224 EZ-Spot ® 8 8 28 Water 28 28 98 Total Volume 100 350

The spotting fluid composition was also tested against a secondcommercial spotting fluid that included the Pipe-Lax® commercialadditive manufactured by M-I Swaco of Pleasanton, Tex., USA. The secondcommercial spotting fluid compositions for use in the field (in theamount of 100 bbl) and the laboratory (in the amount of 350 cc) areshown in Table 3:

TABLE 3 Formulation of Second Commercial Spotting Fluid FieldFormulation Concentration Lab Formulation Components (bbl) (volume %)(cc) Diesel 64 64 224 Pipe-Lax 8 8 28 Water 28 28 98 Total Volume 100350

The alkyl ester spotting fluid composition, the first commercialspotting fluid, and the second commercial spotting fluid were testedusing a simulation of various elements of pipe sticking and stuck piperecovery operation using a sample potassium chloride (KCl)-polymermudcake.

Initially, the sticking bond modulus (SBM) and ultimate sticking bondstrength (USBS) of the mudcake were determined before interaction withany spotting fluid. FIG. 1 depicts a process 100 for determining the SBMand USBS of a mudcake before interaction with any spotting fluid.Initially, the mudcake having a thickness of 10 millimeters (mm) or lesswas prepared (block 102). Next, a spherical foot was embedded into themudcake to simulate pipe sticking (block 104). The spherical foot andmudcake were allowed to stabilize and form bonds over a time period oftwo minutes (block 106).

A pulling force was then applied to unstick the spherical foot andsimilar a pipe recovery operation (block 108) and a force-displacementgraph was generated. The SBM of the original mudcake was determined fromthe slope of the initial linear portion of the force-displacement graph(block 110). Additionally, the USBS of the original mudcake wasdetermined from the peak value of the force-displacement graph (block112).

After determining the SBM and USBS of the mudcake before interactionwith any spotting fluid, the SBM and USBS using the spotting fluidcomposition, the first commercial spotting fluid, and the secondcommercial fluid to unstick the mudcake were determined. FIG. 2 depictsa process 200 for determining the SBM and USBS of a mudcake afterinteraction with the example alkyl ester spotting fluid composition andthe commercial spotting fluid compositions. Initially, the mudcakehaving a thickness of 10 millimeters (mm) or less was prepared (block202). Next, a spherical foot was embedded into the mudcake to simulatepipe sticking (block 204). One of the tested spotting fluids was thenintroduced into the spherical foot-mudcake contact zone (block 206). Themudcake and spotting fluid were allowed to interact over a soaking timeperiod (block 208).

A pulling force was then applied to unstick the spherical foot andsimilar a pipe recovery operation (block 210) and a force-displacementgraph was generated. The SBM associated with the tested spotting fluidwas determined from the slope of the initial linear portion of theforce-displacement graph (block 212). Additionally, the USBS associatedwith the tested spotting fluid was determined from the peak value of theforce-displacement graph (block 214).

According to the procedures described supra, FIGS. 3-6 depict variousgraphs of the pulling force (in kilogram-force (kgf)) vs. displacement(in mm) for the original mudcake without interaction with spottingfluid, the first commercial spotting fluid composition, and the secondcommercial spotting fluid composition, the alkyl ester spotting fluidcomposition. Thus, FIGS. 3-6 each show a force-displacement curvegenerated during the testing procedure described supra. For example,FIG. 3 shows a force-displacement curve without interaction with aspotting fluid, FIGS. 4A and 4B show force-displacement curvesassociated with the first commercial spotting fluid composition, FIGS.5A and 5B show force-displacement curves associated with the secondcommercial spotting fluid composition, and FIGS. 6A and 6B show loaddisplacement curves associated with the/alkyl ester spotting fluidcomposition. The humps and variations in the force-displacement curvesmay correspond to momentary build-ups and failures of sticking bonds dueto weak points and links between the spherical foot and the mudcake.

FIG. 3 depicts a graph 300 of the pulling force (as shown on the x-axis302) vs. displacement (as shown on the y-axis 304) for unsticking thespherical foot from the mudcake without interaction with a spottingfluid. The plot 300 depicts three force displacement curves thatcorrespond to three tests conducted on the mudcake without interactionwith a spotting fluid. As shown in FIG. 3, unsticking the spherical footfrom the mudcake without interaction with a spotting fluid requires atleast 5 kgf of force. The average USBS determined from the peaks of thethree force-displacement curves is about 6.014. The average SBMdetermined from the slopes of the initial linear portions of the threeforce-displacement curves shown in FIG. 3 is about 38.241 kgf/mm

FIGS. 4A and 4B depict various graphs of the pulling force vs.displacement for unsticking the spherical foot from the mudcake in thepresence of the first commercial spotting fluid composition. FIG. 4Adepicts a plot 400 of the pulling force (as shown on the x-axis 402) vs.displacement (as shown on the y-axis 404) after a soaking time period ofsix hours. The plot 400 depicts three force-displacement curves thatcorrespond to three tests conducted using a mudcake and the firstcommercial spotting fluid composition. As shown in FIG. 4A, unstickingthe spherical foot from the mudcake after soaking with the firstcommercial spotting fluid composition for a time period of 6 hoursrequires at least about 2.5-3 kgf of force. The average USBS determinedfrom the peaks of the three force-displacement curves of FIG. 4A isabout 2.81. The average SBM determined from the slopes of the initiallinear portions of the three force-displacement curves shown in FIG. 4Ais about 33.92 kgf/mm.

Similarly, FIG. 4B depicts a plot 406 of the pulling force (as shown onthe x-axis 408) vs. displacement (as shown on the y-axis 410) after asoaking time period of sixteen hours. Here again, the plot 406 depictsthree force-displacement curves that correspond to three tests conductedusing a mudcake and the first commercial spotting fluid composition. Asshown in FIG. 4B, unsticking the spherical foot from the mudcake aftersoaking with the first commercial spotting fluid composition for a timeperiod of 16 hours requires at least about 1.4-1.6 kgf of force. Theaverage USBS determined from the peaks of the three force-displacementcurves of FIG. 4B is about 1.497, and the average SBM determined fromthe slopes of the initial linear portions of the threeforce-displacement curves shown in FIG. 4B is about 22.276 kgf/mm

FIGS. 5A and 5B depict various plot of the pulling force vs.displacement for unsticking the spherical foot from the mudcake in thepresence of the second commercial spotting fluid composition. FIG. 5Adepicts a plot 500 of the pulling force (as shown on the x-axis 502) vs.displacement (as shown on the y-axis 504) after a soaking time period ofsix hours. The plot 500 depicts three force-displacement curves thatcorrespond to three tests conducted using a mudcake and the secondcommercial spotting fluid composition. As shown in FIG. 5A, unstickingthe spherical foot from the mudcake after soaking with the secondcommercial spotting fluid composition for a time period of 6 hoursrequires at least about 1.2-1.3 kgf of force. The average USBSdetermined from the peaks of the three force-displacement curves of FIG.5A is about 1.272. The average SBM determined from the slopes of theinitial linear portions of the three force-displacement curves shown inFIG. 5A is about 22.678 kgf/mm.

Similarly, FIG. 5B depicts a plot 506 of the pulling force (as shown onthe x-axis 508) vs. displacement (as shown on the y-axis 510) after asoaking time period of sixteen hours. The plot 506 thus depicts threeforce-displacement curves that correspond to three tests conducted usinga mudcake and the first commercial spotting fluid composition. As shownin FIG. 5B, unsticking the spherical foot from the mudcake after soakingwith the second commercial spotting fluid composition for a time periodof 16 hours requires at least about 1.6-1.8 kgf of force. The averageUSBS determined from the peaks of the three force-displacement curves ofFIG. 5B is about 1.745, and the average SBM determined from the slopesof the initial linear portions of the three force-displacement curvesshown in FIG. 5B is about 30.427 kgf/mm.

Finally, FIGS. 6A and 6B depict various plot of the pulling force vs.displacement for unsticking the spherical foot from the mudcake in thepresence of the alkyl ester spotting fluid composition. FIG. 6A depictsa plot 600 of the pulling force (as shown on the x-axis 602) vs.displacement (as shown on the y-axis 604) after a soaking time period ofsix hours. The plot 600 depicts three force-displacement curves thatcorrespond to three tests conducted using a mudcake and the secondcommercial spotting fluid composition. As shown in FIG. 6A, unstickingthe spherical foot from the mudcake after soaking with the alkyl esterspotting fluid composition for a time period of 6 hours requires atleast about 1.4-1.5 kgf of force. The average USBS determined from thepeaks of the three force-displacement curves of FIG. 6A is about 1.447.The average SBM determined from the slopes of the initial linearportions of the three force-displacement curves shown in FIG. 6A isabout 25.878 kgf/mm.

FIG. 6B depicts a plot 606 of the pulling force (as shown on the x-axis608) vs. displacement (as shown on the y-axis 610) after a soaking timeperiod of sixteen hours. Thus, the plot 606 thus depicts threeforce-displacement curves that correspond to three tests conducted usinga mudcake and the first commercial spotting fluid composition. As shownin FIG. 6B, unsticking the spherical foot from the mudcake after soakingwith the alkyl ester commercial spotting fluid composition for a timeperiod of 16 hours requires at least about 1.6 kgf of force. The averageUSBS determined from the peaks of the three force-displacement curves ofFIG. 6B is about 1.614, and the average SBM determined from the slopesof the initial linear portions of the three force-displacement curvesshown in FIG. 6B is about 26.361 kgf/mm.

Tables 4-10 depict the SBM and USBS values for unsticking the mudcakewithout interaction with a spotting fluid, for unsticking the sphericalfoot from the mudcake in the presence of the first commercial spottingfluid composition, for unsticking the spherical foot from the mudcake inthe presence of the second commercial spotting fluid composition, andfor unsticking the mudcake in the presence of the alkyl ester spottingfluid composition, as derived from the graphs illustrated in FIGS. 4-6and described supra.

Table 4 depicts the SBS and USBS for unsticking the mudcake withoutinteraction with a spotting fluid:

TABLE 4 SBS and USBS for the mudcake without interaction with a spottingfluid Fit SBM (kgf/mm) USBS (kgf) Test 1 0.999 40.732 6.347 Test 2 0.99736.927 5.933 Test 3 0.997 37.065 5.761 Average 0.998 38.241 6.014Standard 0.001 2.158 0.301 Deviation (S.D.) Coefficient of 0.130 5.8335.152 Variation

Table 5 depicts the SBS and USBS for unsticking the mudcake in thepresence of the first commercial spotting fluid composition after asoaking time period of six hours:

TABLE 5 SBS and USBS for the mudcake in the presence of the firstcommercial spotting fluid composition after 6 hours Fit SBM (kgf/mm)USBS (kgf) Test 1 0.991 33.349 3.11 Test 2 0.992 33.186 2.87 Test 30.974 35.213 2.46 Average 0.99 33.92 2.81 Standard 0.01 1.13 0.33Deviation (S.D.) Coefficient of 1.05 3.32 11.68 Variation

Table 6 depicts the SBS and USBS for unsticking the mudcake in thepresence of the first commercial spotting fluid composition after asoaking time period of sixteen hours:

TABLE 6 SBS and USBS for the mudcake in the presence of the firstcommercial spotting fluid composition after 16 hours Fit SBM (kgf/mm)USBS (kgf) Test 1 0.992 17.107 1.485 Test 2 0.985 24.652 1.4338 Test 30.990 25.0707 1.571 Average 0.989 22.276 1.497 Standard 0.004 4.4820.069 Deviation (S.D.) Coefficient of 0.333 20.120 4.617 Variation

Table 7 depicts the SBS and USBS for unsticking the mudcake in thepresence of the second commercial spotting fluid composition after asoaking time period of six hours:

TABLE 7 SBS and USBS for the mudcake in the presence of the secondcommercial spotting fluid composition after 6 hours Fit SBM (kgf/mm)USBS (kgf) Test 1 0.983 22.348 1.262 Test 2 0.984 21.077 1.231 Test 30.989 24.610 1.324 Average 0.985 22.678 1.272 Standard 0.003 1.790 0.047Deviation (S.D.) Coefficient of 0.318 7.891 3.726 Variation

Table 8 depicts the SBS and USBS for unsticking the mudcake in thepresence of the second commercial spotting fluid composition after asoaking time period of sixteen hours:

TABLE 8 SBS and USBS for the mudcake in the presence of the secondcommercial spotting fluid composition after 16 hours Fit SBM (kgf/mm)USBS (kgf) Test 1 0.993 28.835 1.825 Test 2 0.993 30.706 1.758 Test 30.994 31.739 1.653 Average 0.993 30.427 1.745 Standard 0.001 1.472 0.087Deviation (S.D.) Coefficient of 0.083 4.839 4.962 Variation

Table 9 depicts the SBS and USBS for unsticking the mudcake in thepresence of the alkyl ester spotting fluid composition after a soakingtime period of six hours:

TABLE 9 SBS and USBS for the mudcake in the presence of the alkyl esterspotting fluid composition after 6 hours Fit SBM (kgf/mm) USBS (kgf)Test 1 0.988 25.050 1.4827 Test 2 0.989 26.232 1.4519 Test 3 0.99026.353 1.4073 Average 0.989 25.878 1.447 Standard 0.001 0.720 0.038Deviation (S.D.) Coefficient of 0.084 2.783 2.619 Variation

Table 10 depicts the SBS and USBS for unsticking the mudcake in thepresence of the alkyl ester spotting fluid composition after a soakingtime period of sixteen hours:

TABLE 10 SBS and USBS for the mudcake in the presence of the alkyl esterspotting fluid composition after 16 hours Fit SBM (kgf/mm) USBS (kgf)Test 1 0.970 28.261 1.6025 Test 2 0.991 25.387 1.6074 Test 3 0.98925.434 1.6315 Average 0.983 26.361 1.614 Standard 0.012 1.646 0.016Deviation (S.D.) Coefficient of 1.180 6.245 0.962 Variation

FIGS. 7-10 are various bar graphs comparing the SBM and USBS describedin Tables 7-10. FIG. 7 depicts a bar graph 700 that shows a comparisonof the average SBMs (in kgf/mm) of the mudcake without interaction withany spotting fluids and for the first commercial spotting fluidcomposition, the second commercial spotting fluid composition, and thealkyl ester spotting fluid composition. FIG. 8 depicts a bar graph 800illustrating the percentage reduction in SBM associated with the alkylester and the percentage reduction in SBM associated with the commercialspotting fluids, as compared to the SBM for the mudcake withoutinteraction with any spotting fluid.

As shown in FIG. 7, each of the tested spotting fluids reduce thesticking bond modulus of the mudcake due to the interactions of thespotting fluids and the effect on the sticking bonds between the mudcakeand the spherical foot. As also shown in FIGS. 7 and 8, the alkyl esterspotting fluid composition showed a larger reduction in SBM values for asix hour soaking time period than the first commercial spotting fluidwhile having nearly comparable reduction in SBM values to the secondcommercial spotting fluid. For example, the SBM value associated withthe alkyl ester spotting fluid composition is nearly equal to the SBMvalue associated with the second commercial spotting fluid composition.Additionally, as shown in FIG. 7, the second commercial spotting fluidshowed an increased in SBM after the sixteen hour soaking time period,indicating that the second commercial spotting fluid may have a timedependent stiffening effect that causes an increase in SBM.Consequently, using the second commercial spotting fluid and soakingbeyond an optimal time period may increase the difficulty of recoveringa stuck pipe. In contrast, the alkyl ester spotting fluid compositionshowed no time-dependent stiffening effect and thus showed superiorlong-term behavior as compared to the second commercial spotting fluid.As shown supra, the alkyl ester spotting fluid composition caused adegradation and weakening of sticking bonds within a relatively shorttime period (the six hour soaking time period), showing superiorshort-term behavior as compared to the first commercial spotting fluidcomposition.

FIG. 9 depicts a bar graph 900 that shows a comparison of the averageUSBS's (in kgf) of the mudcake without interaction with any spottingfluids and for the first commercial spotting fluid composition, thesecond commercial spotting fluid composition, and the alkyl esterspotting fluid composition. FIG. 10 depicts a bar graph 1000illustrating the percentage reduction in USBS associated with the alkylester and the percentage reduction in USBS associated with thecommercial spotting fluids, as compared to the USBS for the mudcakewithout interaction with any spotting fluid.

As shown in FIG. 9, each of the tested spotting fluids reduces the USBSof the mudcake due to the interactions of the spotting fluids and theeffect on the sticking bonds between the mudcake and the spherical foot.As also shown in FIGS. 9 and 10, the alkyl ester spotting fluidcomposition showed a larger reduction in USBS values for a six hoursoaking time period than the first commercial spotting fluid whilehaving nearly comparable reduction in USBS values to the secondcommercial spotting fluid. For example, the USBS value associated withthe alkyl ester spotting fluid composition is nearly equal to the USBSvalue associated with the second commercial spotting fluid composition.Additionally, as shown in FIG. 9, the second commercial spotting fluidshowed an increased in USBS after the sixteen hour soaking time period.The increase in both SBM and USBS showed by the second commercialspotting fluid confirms that the second commercial spotting fluidcomposition has a time-dependent stiffening and hardening effect.Consequently, a soaking time period greater than an optimal soaking timeperiod may increase the difficulty of recovering the stuck pipe. Hereagain, the USBS values shown in FIGS. 9 and 10 demonstrate that thealkyl ester spotting fluid composition has no time dependent stiffeningand hardening effect and has superior long-term behavior as compared tothe second commercial spotting fluid. Similarly, the USBS values alsoconfirm that the alkyl ester spotting fluid composition has improvedshort-term behavior as compared to the first commercial spotting fluid.

Alkyl Ester Spotting Fluid Compositions

In some embodiments, an alkyl ester spotting fluid composition caninclude an invert emulsion having an alkyl ester as the external phaseand water as the internal phase. The internal phase can includefreshwater (water having relatively low (that is, less than 5000 ppm)concentrations of total dissolved solids) or seawater (for example,water having a salinity in the range of about 33,000 to about 37,000parts-per-million (ppm)). In some embodiments, the internal phase mayinclude artificial brines, natural brines, brackish water, or formationwater. In some embodiments, the volumetric ratio of alkyl ester to watercan be in the range of about 95:5 to about 60:40. In some embodiments,the alkyl ester can include an oleic sunflower oil ester (for example, alow oleic sunflower oil ester (70% or less oleic acid) or a high oleicsunflower oil ester (greater than 70% oleic acid), a canola oil ester, ajojoba oil ester, or a castor oil ester. In some embodiments, the alkylester can be produced from a vegetable oil such as sunflower oil, jojobaoil, canola oil, castor oil, palm oil, soybean oil, or other suitablevegetable oils.

In some embodiments, the alkyl ester spotting fluid composition caninclude an invert emulsion having an alkyl ester as the external phaseand water as the internal phase, and an emulsifier. In some embodiments,the emulsifier can be in the range of about 8% to about 9% by volume. Insome embodiments, the emulsifier can include a commercial pipe-freeingagent. In some embodiments, the emulsifier can include EZ Spot®manufactured by Halliburton of Houston, Tex., USA. In some embodiments,the emulsifier can include other suitable emulsifiers, such as Pipe-Lax®manufactured by M-I Swaco of Pleasanton, Tex., USA, EZ MUL® manufacturedby Halliburton of Houston, Tex., USA, XPLOR® 1653 and XPLOR® 1654manufactured by Georgia-Pacific of Atlanta, Ga., USA, GLO PEMUL 1000manufactured by Global Drilling Fluids and Chemical Limited of Gujarat,India, and MUL-EASE I and U-MUL-22 manufactured by Unique DrillingFluids of Dallas, Tex. In some embodiments, the alkyl ester spottingfluid composition can include 64% by volume of an alkyl ester, 8% byvolume of an emulsifier, and 28% by volume of water.

In some embodiments, the alkyl ester spotting fluid composition caninclude a weighting agent, such as barite, calcium carbonate,hausmannite ore, or other suitable weighting agents, to from a spottingfluid composition having a desired weight. In some embodiments, theweighting agent added to the alkyl ester spotting fluid composition caninclude Micromax® weight additives manufactured by Halliburton ofHouston, Tex., USA.

In some embodiments, the alkyl ester spotting fluid composition has a 96hour LC₅₀ of greater than 100,000 parts-per-million (ppm). As usedherein, LC₅₀ refers to the lethal concentration (LC) of a chemical oradditive in water which cases the death of 50% or a group of testsubjects. The alkyl ester spotting fluid composition described in thedisclosure can be biodegradable, environmentally friendly, andnon-toxic. For example, vegetable esters produced from vegetable oilsused in the alkyl ester spotting fluid composition may be biodegradable,eco-friendly, and non-toxic. Moreover, due to the biodegradable andenvironmentally friendly properties of the alkyl ester spotting fluid,the alkyl ester spotting fluid may not be removed from a mud systemafter recovering the stuck pipe. In some embodiments, the alkyl esterspotting fluid composition can be incorporated in a water-based mudwithout negatively impacting the environmental characteristics of thewater-based mud. The elimination of the removal phase of the alkyl esterspotting fluid composition will reduce the time and cost associated withfreeing a differentially stuck pipe.

In some embodiments, the alkyl ester spotting fluid composition can beadded to a circulating mud volume in a range of about 2% to about 4% byvolume of the total operating mud system. For example, in someembodiments, about 50 bbl to about 100 bbl of alkyl ester spotting fluidpill can be added to a circulating mud volume of 2500 barrels or more.Additionally, the addition of about 2% to about 4% by volume of thealkyl ester spotting fluid composition can improve the lubricity of awater-based mud and, thus, aid in reducing torque and drag problems indeviated and horizontal boreholes without an adverse effect on thesurrounding environment.

FIG. 11 depicts a process 1100 for using an alkyl ester spotting fluidcomposition in accordance with an embodiment of the disclosure.Initially, the alkyl ester spotting fluid composition can be prepared(block 1102), such as by preparing an invert emulsion having the alkylester as the external phase and water as an internal phase. In someembodiments, preparing the alkyl ester spotting fluid composition caninclude mixing the invert emulsion with an emulsifier. In someembodiments, preparing the alkyl ester spotting fluid composition caninclude mixing the invert emulsion (and in some embodiments, anemulsifier) with a weighting agent.

Next, the spotting fluid composition having an invert emulsion of analkyl ester and water can be introduced (for example, pumping downhole)in the vicinity of a differentially stuck pipe (block 1104). Forexample, the alkyl ester spotting fluid compositing can be added to amud system and circulated downhole with the mud. In some embodiments,the alkyl ester spotting fluid composition can be added in the range ofabout 2% of 4% by volume of the total circulating mud system volume.

In some embodiments, the spotting fluid composition can be allowed tosoak for a time period (block 1106). For example, the spotting fluidcomposition can interact with the material (for example, mudcake)surrounding the stuck pipe.

After a soaking time period, he freed pipe can then be recovered (block1108), such as by removing the freed pipe from the wellbore. In someembodiments, the alkyl ester spotting compositing may not be removedfrom the mud system after recovering the stuck pipe. Thus, in someembodiments a process for removing a stuck pipe using the alkyl esterspotting fluid composition can be performed without removing the alkylester from the mud system.

Ranges may be expressed in the disclosure as from about one particularvalue, to about another particular value, or both. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value, to the other particular value, or both, along withall combinations within said range.

Throughout this application, where patents or publications arereferenced, the disclosures of these references in their entireties areintended to be incorporated by reference into this application, in orderto more fully describe the state of the art to which the disclosurepertains, except when these references contradict the statements made inthe disclosure.

Further modifications and alternative embodiments of various aspects ofthe disclosure will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the embodiments described inthe disclosure. It is to be understood that the forms shown anddescribed in the disclosure are to be taken as examples of embodiments.Changes may be made in the elements described in the disclosure withoutdeparting from the spirit and scope of the disclosure as described inthe following claims. Headings used in the disclosure are fororganizational purposes only and are not meant to be used to limit thescope of the description.

What is claimed is:
 1. A spotting fluid composition for freeingdifferentially stuck pipe in a well, the spotting fluid compositioncomprising: an emulsifier; an invert emulsion including: an externalphase comprising an alkyl ester produced from the esterification of avegetable oil; and an internal phase comprising water.
 2. The spottingfluid composition of claim 1, wherein the alkyl ester comprises at leastone of an oleic sunflower oil ester, a canola oil ester, a jojoba oilester, and a castor oil ester.
 3. The spotting fluid composition ofclaim 1, wherein the invert emulsion consists of: the external phasecomprising the alkyl ester; and the internal phase comprising water. 4.The spotting fluid composition of claim 1, wherein the external phaseconsists of the alkyl ester and the internal phase consists of water. 5.The spotting fluid composition of claim 1, wherein a volumetric ratio ofthe alkyl ester to water is in a range of 95:5 to 60:40.
 6. The spottingfluid composition of claim 1, wherein the emulsifier comprises at least8% by volume.
 7. The spotting fluid composition of claim 1, wherein thealkyl ester comprises at least 60% by volume, the emulsifier comprisesat least 8% by volume, and water is no more than 32% by volume.
 8. Thespotting fluid composition of claim 1, comprising a weighting agent. 9.The spotting fluid composition of claim 8, wherein the weighting agentcomprises at least one of barite, calcium carbonate, and hausmanniteore.
 10. A method of freeing differentially stuck pipe in a well,comprising: introducing a spotting fluid composition in the vicinity ofa portion of differentially stuck pipe, such that the spotting fluidcontacts a material surrounding the portion of differentially stuckpipe, the spotting fluid composition comprising: an emulsifier; aninvert emulsion including: an external phase comprising an alkyl esterproduced from the esterification of a vegetable oil; and an internalphase comprising water;
 11. The method of claim 10, wherein the alkylester comprises at least one of an oleic sunflower oil ester, a canolaoil ester, a jojoba oil ester, and a castor oil ester.
 12. The method ofclaim 10, wherein the invert emulsion consists of: the external phasecomprising the alkyl ester; and the internal phase comprising water. 13.The method of claim 10, wherein the external phase consists of the alkylester and the internal phase consists of water.
 14. The method of claim10, comprising allowing the spotting fluid composition to interact withthe material surrounding the portion of differentially stuck pipe over atime period.
 15. The method of claim 10, comprising adding the spottingfluid composition to a mud system configured to circulate a drillingmud.
 16. The method of claim 15, wherein the spotting fluid compositionis added to the mud system in a range of 2% to 4% by volume.
 17. Themethod of claim 15, comprising: recovering the stuck pipe; and retainingthe spotting fluid composition in the mud system after recovering thestuck pipe.
 18. The method of claim 10, wherein a volumetric ratio ofthe alkyl ester to water is in a range of 95:5 to 60:40.
 19. The methodof claim 10, wherein the emulsifier comprises at least 8% by volume. 20.The method of claim 10, comprising a weighting agent.
 21. A method offorming a spotting fluid composition for freeing differentially stuckpipe, comprising: preparing an invert emulsion, the invert emulsionincluding: an external phase comprising an alkyl ester produced from theesterification of a vegetable oil; and an internal phase comprisingwater; adding an emulsifier to the invert emulsion to form the spottingfluid composition.
 22. The method of claim 21, wherein the alkyl estercomprises at least one of an oleic sunflower oil ester, a canola oilester, a jojoba oil ester, and a castor oil ester.
 23. The method ofclaim 21, wherein the external phase consists of the alkyl ester and theinternal phase consists of water.
 24. The method of claim 21, wherein avolumetric ratio of the alkyl ester to water is in a range of 95:5 to60:40.
 25. The method of claim 21, wherein the emulsifier comprises atleast 8% by volume.
 26. The method of claim 21, comprising adding aweighting agent.
 27. The method of claim 26, wherein the weighting agentcomprises at least one of barite, calcium carbonate, and hausmanniteore.